1. Field of the Invention
The present invention relates to a wideband optical fiber amplifier. More particularly, the present invention is directed to a wideband optical fiber amplifier for amplifying optical signals transmitted from an optical communication network under a predetermined condition, thereby compensating for a loss of optical signals or a reduction of optical power.
2. Description of the Related Art
A conventional optical fiber amplifier, used in an optical communication system, is a device for amplifying various transmitted optical signals. The optical fiber amplifier amplifies optical signals as they are without photoelectric transformation. This allows for a simple, economical construction. The optical fiber amplifier includes an optical fiber doped with at least one rare-earth element, a pumping diode for generating pumping lights, a wavelength selection coupler for providing combination of transmitted optical signals with the pumping lights to the doped optical fiber, and an optical isolator.
Various rare-earth elements dopes for the optical fiber may be used, e.g., erbium (Er), praseodymium (Pr), neodymium (Nd) and the like.
Optical amplification using the rare-earth element doped optical fiber is carried out through a stimulated emission process. Pumping lights emitted from a pumping diode carry out exciting and ionizing of a rare-earth element doped into optical fiber. As a result, optical signals transmitted into the rare-earth element doped optical fiber are amplified by stimulated emission of the excited ions.
With the gradual increase in the amounts of data transmitted through optical communication systems, the demand to broaden transmission bandwidths of optical communication networks has increased. In response to this demand, wideband optical fiber amplifiers, for a wavelength division multiplex in optical communication systems, which can simultaneously make use of C-band optical signals ranged from 1530 nm to 1560 nm and L-band optical signals ranged from 1570 nm to 1600 nm are commonly employed.
FIG. 1 shows a construction of a conventional wideband optical fiber amplifier 100. The wideband optical fiber amplifier 100 includes a C/L splitter 110, a three-port optical circulator 111, first and second amplification sections 130 and 140, optical isolators 113, 121 and 125, and first and second optical signal couplers 115 and 123.
The C/L splitter 110 separates input wideband optical signals, which have been transmitted from an optical communication network to the wideband optical fiber amplifier 100, into C-band optical signals and L-band optical signals The separated C-band optical signals and L-band optical signals are then transmitted to the first amplification section 130 and the second amplification section 140, respectively.
The three-port optical circulator 111 is provided with a first port, a second port and a third port. The C-band optical signals are received through the first port. The received C-band optical signals are output through the second port to the first amplification section 130The second port may also receive amplified spontaneous emissions (ASEs) which are generated from the first amplification section 130. The received ASEs are output through the third port to the second optical coupler 123. The optical circulator 111 also prevents spontaneous emissions input through the second port or reflected optical signals from being reversely output through the first port, and thus functions as an optical isolator.
The first amplification section 130 includes a first pumping diode 131, a first wavelength selection coupler 132 and a rare-earth element doped optical fiber 133, acting to amplify the C-band optical signals inputted from the optical circulator 111. Pumping lights generated from the first pumping diode 131 are combined with the C-band optical signals at the first wavelength selection coupler 132 and then input into the rare-earth element doped optical fiber 133. A rare-earth element doped into the rare-earth element doped optical fiber 133 is excited by the pumping lights and then amplifies the C-band optical signals under a stimulated emission. The first pumping diode 131 may use a laser diode that outputs pumping lights having a wavelength band of about 980 nm or 1480 nm. Spontaneous emission generated during an optical signal amplification of the first amplification section 130 are input into the second port of the optical circulator 111 and then directed through the third port of the optical circulator 111 to the second amplification section 140. These spontaneous emissions generated from the first amplification section 130 are supplied as pumping lights for the second amplification section 140.
The C-band optical signals amplified by the first amplification section 130 are then input through the optical isolator 113 into the first optical signal coupler 115.
The L-band optical signals separated by the C/L splitter 110 are input through the optical isolator 121 and the second optical signal coupler 123 into the second amplification section 140. The separated L-band optical signals are then amplified by the second amplification section 140.
The second optical coupler 123 combines the separated L-band optical signals with the spontaneous emissions input from the optical circulator 111, and then inputs the combined results into the second amplification section 140. As mentioned above, the spontaneous emissions generated from first amplification section 130 are supplied as pumping lights for the second amplification section 140.
The second amplification section 140 includes second and third pumping diodes 141a and 141b, second and third wavelength selection couplers 143a and 143b, and a rare-earth element doped optical fiber 145, acting to amplify the separated L-band optical signals.
Pumping lights generated from the second and third pumping diodes 141a and 141b are input through each of the wavelength selection couplers 143a and 143b into the rare-earth element doped optical fiber 145. As noted above, the spontaneous emissions generated from the first amplification section 130 are used as pumping lights for amplifying the L-band optical signals. A rare-earth element doped into the rare-earth element doped optical fiber 145 is excited by the pumping lights and then amplifies the L-band optical signals under a stimulated emission. Each of the second and third wavelength couplers 143a and 143b is provided on the corresponding input and output sides of the second amplification section 140, inputting the pumping lights into the rare-earth element doped optical fiber 145 from both sides of the second amplification section 140.
The L-band optical signals amplified by the second amplification section 140 are input through the optical isolator 125 into the first optical signal coupler 115.
The first optical coupler 115 combines the C-band optical signals and the L-band optical signals amplified by each of the fist and second amplification sections 130 and 140, respectively, and then outputs the combined results to the optical communication network (not shown).
However, as mentioned above, since the conventional wideband optical fiber amplifier uses an additional optical signal coupler to separate wideband optical signals input first from the optical communication network into C-band optical signals and L-band optical signals and then to amplify each of the separated two band optical signals, it has various problems. For example, a noise figure as well as an insertion loss is increase. In addition, the cost of manufacture is increased due to the increased number of components to be constructed.
Accordingly, there is an need in the art for an improved optical signal amplification system.